System, Method and Storage Medium for a Multi-Mode Memory Buffer Device

1. A buffer device for providing multiple operating modes, the buffer device comprising: a first memory interface adapted to connect the buffer device to a cascaded interconnect system through an upstream memory bus and a downstream memory bus, wherein the buffer device receives one or more clock inputs; and a second memory interface which includes one or more second clock lines for driving one or more second clocks derived from the one or more clock inputs, the second memory interface having two or more selectable modes of operation including: a first mode of operation for connecting the buffer device to one or more synchronous memory devices located on a first memory assembly which includes the buffer device; and a second mode of operation for connecting the buffer device to one or more second memory assemblies, the second memory assemblies including one or more of unbuffered and registered memory assemblies, wherein at least one of the second memory assemblies requires that the buffer device communicate with the second memory assembly using drive strength and timing characteristics that differ from those used to communicate with the synchronous memory devices connected to the first memory assembly in the first mode of operation, the timing characteristics including one or more of read data, write data, address and command timing relationships relative to the one or more second clocks.

2. The buffer device of claim 1 wherein one of the second memory assemblies is an unbuffered memory assembly.

3. The buffer device of claim 2 wherein the timing characteristics further include read or write data relative to one of the second clocks.

4. The buffer device of claim 1 wherein one of the second memory assemblies is a registered memory assembly.

5. The buffer device of claim 4 wherein in the second mode of operation there is a reduced drive strength for the addresses relative to the first mode of operation.

6. The buffer device of claim 1 wherein the buffer device is operable with two or more registered memory assemblies or two or more unbuffered memory assemblies.

7. The buffer device of claim 1 wherein one of the second clocks is redriven on the registered memory assemblies.

8. The buffer device of claim 7 wherein the registered memory assembly provides a maximum of two loads per second clock.

9. The buffer device of claim 1 wherein the buffer device communicates with memory devices that are interconnected to each other using different wiring topologies.

10. The buffer device of claim 1 wherein in the second mode of operation, data arrives at the buffer device at least one clock later in relationship to a command than in the first mode of operation.

11. A buffer device for providing multiple operating modes, the buffer device comprising: a first memory interface adapted to connect the buffer device to a cascaded interconnect system through an upstream memory bus and a downstream memory bus, wherein the buffer device receives one or more clock inputs; and a second memory interface which includes one or more second clock lines for driving one or more second clocks derived from the one or more clock inputs, the second memory interface having two or more selectable modes of operation including: a first mode of operation for connecting the buffer device to one or more synchronous memory devices located on a first memory assembly which includes the buffer device; and a second mode of operation for connecting the buffer device to one or more second memory assemblies, the second memory assemblies including one or more of unbuffered and registered memory assemblies, wherein at least one of the second memory assemblies requires that the buffer device communicate with the second memory assembly using one or both of drive strength and timing characteristics that differ from those used to communicate with the synchronous memory devices connected to the first memory assembly in the first mode of operation, the timing characteristics including one or more of read data, write data, address and command timing relationships relative to the one or more second clocks.

12. The buffer device of claim 11 wherein one of the second memory assemblies is an unbuffered memory assembly.

13. The buffer device of claim 12 wherein the timing characteristics further include read or write data relative to one of the second clocks.

14. The buffer device of claim 11 wherein one of the second memory assemblies is a registered memory assembly.

15. The buffer device of claim 14 wherein in the second mode of operation there is a reduced drive strength for the addresses relative to the first mode of operation.

16. The buffer device of claim 11 wherein the buffer device is operable with two or more registered memory assemblies or two or more unbuffered memory assemblies.

17. The buffer device of claim 11 wherein one of the second clocks is redriven on the registered memory assemblies.

18. The buffer device of claim 17 wherein the registered memory assembly provides a maximum of two loads per second clock.

19. The buffer device of claim 11 wherein the buffer device communicates with memory devices that are interconnected to each other using different wiring topologies.

20. The buffer device of claim 11 wherein in the second mode of operation, data arrives at the buffer device at least one clock later in relationship to a command than in the first mode of operation.